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Question: How often should I replace the 4004 water in-line strainer on my Aprilaire humidifier?

4004 strainer closeup

Question: How often should I replace the 4004 water in-line strainer on my Aprilaire humidifier? 

Answer: We have had this question asked several times before and this is my answer: If it was me, I would only replace the strainer and the restrictor orifice if I was having low water volume coming out of the humidifier supply tube. If water is coming out of the supply tube when the humidifier is on then I would leave it alone because you are asking for more problems when you start turning the saddle valve water valve off / ON and if you allow sediment in to stop up the 4040 solenoid valve. I copied the solenoid valve replacement instructions from our site below. I would recommend always flushing out the saddle valve and water line into a bucket if you ever turn the water off and back on at the saddle valve. Flushing the humidifier water line out makes sure that all the sediment goes into the bucket instead of getting caught in the humidifier’s strainer, orifice, or 4040 solenoid valve. Some contractors recommend replacing the 4004 strainer every 2 to 3 years, but I would only do it when you are experiencing low water volume out of the humidifier. I would try replacing the orifice first before the strainer. We sell the Aprilaire humidifier orifices on the following page: Please click here if you are interested in the Aprilaire humidifier orifices that we sell. We sell the Aprilaire 4004 strainers on the following page: Please click here if you are interested in the 4004 Aprilaire Strainers that we sell. Sometimes the strainers are very hard to get out because of all the sediment that has built up over the years. Some people end up messing the 4040 valves up if they can not remove the strainer properly. Many times the strainer gets stuck and is hard to remove. Please click here if you are interested in the Aprilaire 4040 solenoid valves that we sell.  I also copied a picture below that shows what others recommend on replacing the strainer. If you have any questions please either comment below or email us anytime at

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4004 replacement recommendations
Above 4004 replacement recommendations are every 2 to 3 years:  
4231 restritor orifices
Above Aprilaire 4231 restrictor orifices:
Above 4040 water solenoid  in the Aprilaire bag:

Solenoid Valve Replacement Instructions:

    1. For power units unplug the electrical cord. For bypass, units turn off power to the furnace. Also, turn the humidistat off.
    2. Shut off the water supply at the saddle valve
    3. Disconnect inlet and outlet water compression nuts. Double wrench. Note, some water may drip on the floor. Remove the orifice (which controls the water flow) from the plastic or copper tube and make sure there is no obstruction. If blocked clean or replace.
    4. Remove the wire nuts from the water solenoid valve wire connections. Set aside.
    5. Remove screws that secure the valve to the unit.
    6. Attach a new valve with screws. Do not over-torque screws into the plastic housing.
    7. Reconnect wires with wire nuts.
    8. For units with plastic feed, tubes inspect for brittleness, hairline cracks, nicks or abrasions, etc.  Replace if necessary.
    9. I would highly recommend completing this step while the humidifier water supply line is disconnected to clean out the supply line/saddle valve and make sure that you have a good flow of water coming out of the water supply line. Many times a new valve can become stopped up if this step is not completed. This can be accomplished by taking a bucket, setting the loose humidifier water supply line down into the bucket (two people are best), then turn on the saddle valve to get all loose sediment out of the saddle valve and the waterline. This can be accomplished by allowing the water to run into the bucket for 10 to 15 seconds. If you can not get adequate water flow out of your saddle valve then you will need to replace your saddle valve. We sell a really good Supco saddle valve on the following page: Please click here for the saddle valve we recommend.
    10. Reconnect the water lines, double wrenching the compression nuts.
    11. Turn the water back on and check the system for leaks. Tighten compression nuts as necessary.
    12. Restore electrical service and activate the furnace by turning up the thermostat.
    13. Turn up the humidistat to verify the operation of the humidifier.
    14. Recheck for leaks. Turn down the humidistat to make sure the valve shuts off. Reset humidistat and thermostat to original levels.

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